The present invention relates to an optical module in which optical devices, such as light emitting device and a light receiving device, are integrated with an optical transmission path, such as obtained with fiber optics and optical waveguides, and a process for manufacturing the same.
In an optical module used in optical communication, the optical devices and the optical transmission path included in the module must be closely positioned. Close positioning of the devices assures that an optical signal is accurately transmitted between the optical devices and the optical transmission path.
Japanese Patent Application Laid-Open No. 8-179154 discloses a process for manufacturing such an optical module at a low cost. The disclosed process permits optical devices to be mounted in self-alignment by utilizing the surface tension of a solder bump. In this process, as a first step, a metallized solder joint pad is formed on a silicon substrate with photolithography technology. In the next step, silicon is deposited on the substrate, and patterned to form a planar optical waveguide. Then, formed on the solder joint pad on the substrate is a solder bump on which a semiconductor laser chip formed with a solder joint pad is mounted. Subsequently, the solder bump is made molten so that the semiconductor laser chip is joined to the silicon substrate. The semiconductor laser chip is automatically positioned at a predetermined junction position by a self-alignment effect based on the surface tension of the molten solder bump.
In the process, the optical waveguide and the solder joint pad must be formed using a continuous photolithography process to accurately establish a relative position of the optical waveguide and the solder joint pad formed on the silicon substrate. To this end, the optical waveguide is formed at a high temperature of 800xc2x0 C. or more by a silicon deposition process after the solder joint pad is formed on the substrate. However, if the metallized solder joint pad is exposed to a high temperature during formation of the optical waveguide, it deteriorates and is difficult to join to the solder joint pad. In addition, since the solder joint pad is of a minute size, and directly formed on the silicon substrate, it tends to easily peel off the substrate when subjected to a high temperature. Therefore, positioning the semiconductor laser chip by self-alignment using the solder bump is difficult to attain accurately.
An object of the present invention is to eliminate the above problem, and to provide an optical module which can be accurately and reliably manufactured at a low cost, and to provide a manufacturing process for the same.
The optical module of the present invention comprises a substrate with an optical waveguide, and an optical device located opposite to a section of the optical waveguide, wherein the optical device is secured by a solder bump on a solder joint pad. The solder joint pad is formed on non-solder jointing metallization on the substrate. The optical device has a solder joint pad for joining the solder bump. The solder joint pads on the substrate and the optical device are preferably a plurality of elongated pads, including pads parallel to the optical waveguide with their longitudinal side, and pads perpendicular to the optical waveguide with their longitudinal side, respectively.
The process for manufacturing the optical module of the present invention comprises the steps of forming non-solder jointing metallization on a substrate, forming an optical waveguide on the substrate formed with the non-solder jointing metallization, removing a part of the optical waveguide, forming a solder joint pad on the non-solder jointing metallization, and installing an optical device on the solder joint pad through a solder bump.
According to the present invention, since the solder joint pad on the substrate is formed on the non-solder jointing metallization after the optical waveguide is formed, and is not subject to a high temperature, the solder laser chip is accurately positioned by the self-alignment effect of the solder bump on the solder joint pad.